Horizontal oxidation/anneal furnaces have been widely used in the fabrication of semiconductor devices. As described in U.S. Pat. No. 4,992,044 to Philipossian, it is known to use a scavenger ring exhaust system to capture exhaust gases that escape from the process chamber of a horizontal furnace when the door to such furnace is opened. The scavenger ring comprises an annular chamber surrounding the opening to the process chamber of the furnace, with the radially inner wall of the scavenger ring including a plurality of openings through which exhaust gases are drawn into the chamber. Atmospheric gases are drawn into the scavenger ring at a sufficient volume flow rate to ensure that gases present in the furnace process chamber are not released into the surrounding environment. Evacuation of such exhaust gases is required to protect operators of the furnace as well as adjacent portions of the tool from corrosive exhaust gases present in the process chamber of the furnace.
For a variety of reasons, including conservation of floor space and increased control of oxidation and annealing operations, the semiconductor industry has begun using vertical oxidation/anneal furnaces in place of horizontal oxidation/anneal furnaces. As the size of structures in integrated circuit (IC) chips has continued to decrease, it has, in certain circumstances, become necessary to control the environment surrounding the door of the oxidation/anneal furnace to minimize the contaminate particle count in such region. To this end, sealed chambers having a controlled environment are used beneath vertical oxidation/anneal furnaces, with the process chamber of the furnace being coupled with the controlled environment via a load lock. It tends to be difficult to use a scavenger ring exhaust system surrounding the opening of a furnace process chamber when the furnace is associated with a chamber having a controlled environment because the flow rate of such exhaust system is typically sufficiently great as to "sweep away" the controlled environment.
Challenges exist in designing the exhaust system for furnaces in which high temperature oxidation operations are to be performed due to the presence of gaseous hydrochloric acid (HCl) in the process chamber of such furnaces. As used in the specification, including the claims, "gaseous hydrochloric acid" (also referred to as "gaseous HCl" or "HCl gas") means moist hydrogen chloride vapor. The latter is created when dry hydrogen chloride vapor and steam are introduced into the process chamber of the furnace. The phrase "gaseous hydrochloric acid," as used herein, does not mean liquid hydrochloric acid, although both gaseous hydrochloric acid and liquid hydrochloric acid may exist within a given portion of known exhaust systems for oxidation furnaces.
HCl gases rapidly corrode materials, e.g., stainless steel, of the type used in exhaust systems for high-temperature furnaces where HCl gases are not present. As a result of this corrosion problem, quartz has been used in the fabrication of exhaust systems used with furnaces in which high temperature oxidation operations are to be performed, as disclosed in U.S. Pat. Nos. 4,943,235 to Nakao et al., 4,976,610 to Yates and 5,088,922 to Kakizaki et al.
The Kakizaki et al. reference describes a ganged exhaust system intended for use with a plurality of vertical oxidation furnaces, which exhaust system is designed to minimize variations in flow rate between various portions of the exhaust system. This control of the exhaust flow rate is achieved (1) via a pair of valves positioned in each vertical tube of the exhaust system that are operated based on the manifold pressure in the tube adjacent such valves and (2) by an air intake unit positioned between the valves for coupling the interior of the tube with the atmosphere. The valves are apparently positioned in a portion of the exhaust system where the exhaust gases have cooled sufficiently to condense, with a trap being positioned upstream of the valves to capture condensation. The furnace with which the Kakizaki et al. exhaust system is designed to be used is apparently only intended for negative pressure processes, e.g., oxidation processes, and not positive pressure operations such as annealing. Furthermore, although not shown or described, it appears that a scavenger ring exhaust system is likely used in combination with the Kakizaki et al. exhaust system to prevent the release into the environment of gases present in the process chamber.
Valves have been designed for controlling the flow of exhaust gases in the exhaust systems of high temperature furnaces. One such valve assembly, described in U.S. Pat. No. 5,035,611 to Neubecker et al., includes an elongate member that is designed for axial movement between open and closed positions.